cGnRH II involvement in pyriform cell apoptosis.

We have investigated whether gonadotrophin-releasing hormone (GnRH) is involved in triggering the apoptotic death of pyriforms, the nurse cells that cooperate in oocyte growth during mid- to late previtellogenesis in the lizard Podarcis sicula. Our immunocytochemical analyses demonstrate that pyriforms express GnRH receptors and that, in late previtellogenesis, they are up-regulated by cGnRH II. The hormone however does not trigger receptor synthesis and activation, events that therefore must be under the control of other regulatory factors. Our results also indicate that in vitro treatment of pyriforms with cGnRH II induces DNAse I activation and DNA laddering, clear cytological evidence of apoptosis, but not Fas/Fas-L synthesis or caspase activation. We conclude that cGnRH II is pro-apoptotic to pyriform cells and that it exerts its effects by activating an alternative cell death pathway, probably involving calcium as first messenger and DNase I as first executioner.